Chemical mechanical polishing (CMP) is an effective planarization process utilized in the semiconductor industry for manufacturing wafers of ceramic, silicon, glass, quartz, and metals, including the processes of inter-level dielectric (ILD) and Damascene metallization. Such polishing processes generally entail applying the wafer against a rotating pad made from a durable organic substance such as polyurethane. A slurry containing a chemical capable of breaking down the wafer substance is introduced onto the pad. The slurry additionally contains abrasive particles which act to physically erode the wafer surface. The slurry is continually added to the spinning CMP pad, and the dual chemical and mechanical forces exerted on the wafer cause it to be polished in a desired manner.
Of particular importance to the quality of polishing achieved, is the distribution of the abrasive particles across the surface of the pad. The top of the pad holds the particles, usually by a mechanism such as fibers, or small pores, which provide a friction force sufficient to prevent the particles from being thrown off of the pad due to the centrifugal force exerted by the pad's spinning motion. Therefore, it is important to keep the top of the pad as flexible as possible, to keep the fibers as erect as possible, and to assure that there are an abundance of open pores available to receive new abrasive particles.
One problem with maintaining the top of the pad results from an accumulation of debris from the work piece and the abrasive slurry. This accumulation causes a “glazing” or hardening of the top of the pad, and causes the fibers to mat down, thus making the pad less able to hold new abrasive particles from the ongoing slurry flow. This situation significantly decreases the pad's overall polishing performance. Therefore, attempts have been made to revive the top of the pad by “combing” or “cutting” it with various devices. This process has come to be known as “dressing” or “conditioning” the CMP pad. Many types of devices and processes have been used for this purpose. One such device is a dresser disk with a plurality of superabrasive particles, such as diamond, attached to a surface or substrate.
New dresser disks have sharp superabrasive particles that cut dense, deep asperities into the CMP pad surface. The slurry is effectively held in these deep asperities, resulting in a high polishing rate of the wafer. Through continued use, however, the superabrasive particles in the dresser disk begin to wear, and their tips begin to gradually dull. The dull superabrasive particles do not penetrate into the CMP pad surface as deeply and the cutting grooves becomes wider as the superabrasive particle tips wear down. This wearing effect results in asperities that are wide, sparse, and shallow. CMP pads conditioned with such a dresser disk can no longer effectively hold the slurry, thereby decreasing the polishing rate of the wafer. Superabrasive particles on the dresser disk will continue to wear until they are pressing into the pad without cutting. Also, less effective cutting by the dresser disk causes debris to collect on the CMP pad surface, resulting in uneven polishing and increased wafer scratching.
In view of the foregoing, methods of using and constructing CMP pad dresser disks that achieve optimal dressing results, with maximized efficiency and lifespan continue to be sought.